Myosin Isoforms in Relation to Function in Human Heart

描述（由申请方提供）：左心室中表达的肌球蛋白重链（MHC）亚型是哺乳动物心脏工作能力的主要决定因素。直到最近，流行的观点是成年人心室表达几乎100%的β MHC（一种慢亚型），但当代研究表明，正常人心室表达少量的α MHC（一种快亚型），主要是β MHC背景，而失败的人心室表达100%的β MHC，几乎没有α MHC。从这些结果中产生的问题是，α MHC的表达是否有助于正常人心室中压力的上升速率，以及α MHC的缺失是否有助于人类衰竭心脏的收缩性能降低。该项目将基于以下工作假设来解决这些可能性：少量α MHC的表达显著加速正常心肌中力发展的动力学，相反，α MHC的表达减少有助于心力衰竭中力（压力）发展的动力学抑制。拟定的实验将评估由于（i）啮齿动物心肌中α和β a MHC表达比例的改变对收缩特性的影响，其中通过操纵动物的甲状腺状态改变MHC表达，以及（ii）正常人心脏（供体心脏未用于移植）和衰竭心脏（移植受体的移植心脏）的心肌。力的发展和松弛的速率常数将评估从力的变化后，笼中的钙离子螯合剂的光解。然后将结果用于模拟改变的肌球蛋白亚型表达对大鼠和人心肌中的抽搐动力学和幅度的影响。另外的机械实验将研究α MHC和β MHC在确定心肌的功率和牵张激活反应中的作用。使用MHC-同种型特异性抗体的免疫组织化学和肌肉样品的SDS-PAGE将量化左心室区域中的MHC同种型表达模式，以测试MHC表达与收缩期壁应力相关的想法。这些研究的结果将为人类心力衰竭中心肌功能抑制的机制提供新的见解，并为治疗这种疾病提供新的治疗靶点。

DESCRIPTION (provided by applicant): The myosin heavy chain (MHC) isoforms expressed in the left ventricle are primary determinants of the work capacity of mammalian hearts. Until recently, the prevailing view was that adult human ventricles expressed virtually 100% beta MHC (a slow isoform), but contemporary studies have shown that normal human ventricles express small amounts of alpha MHC (a fast isoform) on a predominantly beta MHC background and that failing human ventricles express 100% beta MHC and virtually no alpha MHC. Questions that arise from these results are whether expression of alpha MHC contributes to the rate of rise of pressure in normal human ventricles and whether loss of alpha MHC contributes to the depressed contractile performance of human failing hearts. This project will address these possibilities based on the working hypothesis that expression of small amounts of alpha MHC significantly speeds the kinetics of force development in normal myocardium, and conversely, reduced expression of alpha MHC contributes to depressed kinetics of force (pressure) development in heart failure. The proposed experiments will assess the effects on contractile properties due to altered ratios of alpha and betaa MHC expression in (i) rodent myocardium in which MHC expression is varied by manipulating thyroid status of the animals and (ii) myocardium from normal human hearts (donor hearts not used for transplant) and failing hearts (explanted hearts from transplant recipients). Rate constants of force development and relaxation will be assessed from changes in force following photolysis of caged Ca 2+ chelators. Results will then be used to model the effects of altered myosin isoform expression on twitch kinetics and amplitude in both rat and human myocardium. Additional mechanical experiments will investigate the roles of alpha MHC and beta MHC in determining the power and stretch activation responses of myocardium. Immunohistochemistry using MHC-isoform specific antibodies and SDS-PAGE of muscle samples will quantify MHC isoform expression patterns in regions of the left ventricle to test the idea that MHC expression varies in relation to systolic wall stress. Results from these studies should provide new insights into mechanisms of depressed myocardial function in human heart failure and should also suggest new therapeutic targets for treatment of this disease.